The goal of this project is the development and application of analytical methods to: (1) establish the structure and purity of new antitumor agents and their metabolites, (2) determine physical and chemical properties of new anticancer drugs, 3 measure drugs and their metabolites in biological samples to elucidate in vitro and in vivo pharmacology and to determine in vivo pharmacokinetics, and 4 study reaction mechanisms of potentially useful synthetic transformations. Mass spectrometry, gas chromatography and high-performance liquid chromatography, either alone or in combination, are emphasized analytical approaches. Current studies (biochemistry, clinical pharmacology, and methods enhancement) are focused on cyclopentenyl cytosine, a carbocyclic nucleoside which is presently undergoing Phase I clinical trial as an antitumor agent. The metabolism, distribution and pharmacokinetics of this drug in humans have been determined after both iv bolus dosing and continuous infusion. A novel cytosine-specific reactions has been employed to make a fluorescent derivative to increase HPLC measurement sensitivity for cytosine nucleosides such as cyclopentenyl cytosine in biological fluids. Biochemical studies have defined endogenous and exogenous biomodulators of the cytotoxicity of this agent. Plasma pseudouridine is being investigated as a biomarker of tumor burden following repeated cycles of treatment in a Phase I patient population.